1. Field of the Invention
The subject invention relates to a magnetostrictive strain sensor for measuring a strain along an axis.
2. Description of the Prior Art
Such magnetostrictive strain sensors are known and examples are disclosed and claimed in Ser. No. 10/423,317 filed Apr. 25, 2003 (DP-307303) and Ser. No. 10/313,660 filed Dec. 6, 2002 (DP-308459), both assigned to the assignee of the subject invention and both incorporated into this disclosure. An inductance coil extends around an axis for establishing a loop of magnetic flux looping axially through the coil and extending around the axis to define a donut shaped ring of magnetic flux surrounding the axis. A core made of a magnetostrictive material, such as a Nickel-Iron alloy, provides a primary path for the magnetic flux in a first portion of the loop of magnetic flux. A magnetic carrier provides a return path for the magnetic flux in a second portion of the loop of magnetic flux as the magnetic flux circles the coil through the core and the carrier. The permeability of the magnetostrictive core, thus the inductance of such a device, is a function of the strain applied to the core along the axis. The coil inductance therefore provides a useful signal.
The coil can be excited with an AC voltage or AC current to induce an alternating magnetic field in the core. This field loops around the coil, and will possibly travel through other elements and materials, such as airgaps, and other matter.